Chronic cell lines which have been transformed by Herpes virus display a new and viral specific thymidine kinase (TK) enzyme. This new activity is readily separated from host cellular activity by electrophoresis on PAGE. It also exhibits biochemical properties which differ from its host enzyme. Studies are now in progress directed toward an identification method by which viral TK activity can be detected in the CSF of patients with neurological diseases thought to be associated with Herpes viruses. Patient studies of other neurological diseases and epileptics are also planned to ascertain any correlation between these diseases and possible association with an earlier or latent infection with a DNA virus.